topic 3 - gas exchange Flashcards
cgp (topic 3A) 60 - 61
what are the two things most gas exchange surfaces have in common
(1) a large surface area
(2) they’re thin (often just one layer of epithelial cells) - this provides a short diffusion pathway across the gas exchange surface
what do single celled organisms absorb and release gas
by diffusion through their outer surface
why is there no need for gas exchange in single celled organisms
because they have a relatively large surface area, a thin surface and a short diffusion pathway (oxygen can take part in biochemical reactions as soon as it diffuses into the cell)
what do fish use for gas exchange
a counter current system
what is the first step of fish using a counter current system for gas exchange
water containing oxygen enters the fish through its mouth and passes out through the gills
what are gill filaments
the soft, red, fleshy, thin plates that extend off the gill arch that make up the gill - through which oxygen is taken into the blood from the water passing through the gills - it increases surface area for gas exchange
what are lamellae
the many tiny structures that cover gill filaments - which increases surface area even more
what do lamellae have that speeds up diffusion
lots of blood capillaries and a thin surface layer of cells
what does the lamellae have that speeds up diffusion
many blood capillaries and a thing surface layer of cells
what is the counter current system in fish
the mechanism in which blood flows through the lamellae in one direction and water flows over in the opposite direction
what does the counter current system maintain in fish
a large concentration gradient between the water and the blood - the concentration of water is always higher than in the blood, so as much oxygen as possible diffuses from the water into the blood
what are trachea
microscopic air filled pipes in insects which are used for gas exchange
what are spiracles
the opening in / pores on the exoskeletons of insects - found on the thorax and abdomen of insect
what doe the trachea branch of into, what does this mean for the insect
smaller tracheoles which have thin, permeable walls and go to individual cells - meaning that oxygen diffuses directly into the respiring cells
what does an insect’s circulatory system not transport
O2
how is CO2 released into the atmosphere from an insect
CO2 from the cells move down into its own concentration gradient towards the spiracles to be released into the atmosphere
what do insects use to move air in and out of the spiracles
rhythmic abdominal movements
what is the main gas exchange surface for plants
the surface of the mesophyll cells in the leaf - have a large surface area
where is the mesophyll cells found
inside the leaf
what are the stomata
pores found on the surface of leaves, typically the lower epidermis - which allow for the exchange of carbon dioxide and oxygen
where are stomata found
in the epidermis
what controls the opening and closing of stomata
guard cells
what does exchanging gases tend to make you lose
water
what do insects do if they are loosing too much water
close their spiracles using muscles
what do insects have that minimise water loss
a waterproof, waxy cuticle all over their body and tiny hairs around their spiracles - both of which reduce evaporation
how does the stomata open and close in plants
water enters the guard cells making them turgid - causing the stomatal pore to open
if the plant becomes dehydrates, guard cells lost water and become flaccid - causing the pore to close
what are xerophytes
plants especially adapted for life in warm, dry or windy habitats where water loss is a problem
what are five examples of xerophytic adaptions
(1) stomata sunk in pits that trap moist air, reducing the concentration gradient of water between the leaf and the air - this reduced the amount of water diffusing out of the leaf and evaporating away
(2) a layer of hairs on the epidermis - to trap moist air round the stomata
(3) curled leaves with the stomata inside - protecting them from wind as windy conditions increase the rate of diffusion and evaporation
(4) a reduced number of stomata - so there’s fewer places for water to escape
(5) waxy, waterproof cuticles on leaves and stems to reduce evaporation
